Proprotein convertases (PCs), such as PC1 and furin, are a ubiquitous super-family of evolutionarily conserved serine proteases responsible for mediating a diverse range of processing steps to generate active proteins and peptides within the cell. As premature protease activity can lead to inappropriate protein activation, sorting, or degradation, PC activity is stringently modulated by N-terminal propeptides that function as Intramolecular Chaperones (IMCs) to initially fold protease domains, and act as catalytic inhibitors. Although they share overlapping specificity, it is the ability of the IMC to act as an inhibitor of its cognate catalytic domain that directs the organelle- and pH-specific activation of PC1 and furin, allowing them to selectively cleave their substrates in compartment-specific manner in vivo. Mutations in IMCs of PC1 and furin underlie the aberrant activities seen in a range of endocrinopathies, including extreme obesity, abnormal glucose homeostasis, as well as cancer and heart disease. Despite devastating consequences on cellular homeostasis, the molecular and cellular determinants that modulate activation of PCs are poorly understood. Using an array of biochemical, biophysical, computational and molecular techniques, the goals of this proposal are to 1) determine how the IMC of PC1 acts as a pH sensor, and 2) develop specific inhibitors of PC1 activity.